Solve for $x$ : $-13 = x - 10$
Add $10$ to both sides: $ \begin{eqnarray} \\ \hphantom{-13 {+ 10}} &\hphantom{=}& \hphantom{x} \\ -13 &=& x - 10 \\ \\ {+10} && {+10} \\ \end{eqnarray} $ $ \begin{eqnarray} \\ -13 {+ 10} &=& x \\ \end{eqnarray} $ Simplify. $ x = -3$